Note: Try this answer if you continue to face the issue even after attempting the steps in @ramsudharsan's answer. If you have not tried following those instructions yet I recommend you to do so since that seems to fix the problem in most cases.
It seems that you have a bad superblock. To fix this:
Firstly, boot into a live CD or USB
Find out your partition number by using
sudo fdisk -l|grep Linux|grep -Ev 'swap'
Then, list all superblocks by using the command:
sudo dumpe2fs /dev/sda2 | grep superblock
sda2 to your drive number
You should get a similar output like this
Primary superblock at 0, Group descriptors at 1-6
Backup superblock at 32768, Group descriptors at 32769-32774
Backup superblock at 98304, Group descriptors at 98305-98310
Backup superblock at 163840, Group descriptors at 163841-163846
Backup superblock at 229376, Group descriptors at 229377-229382
Backup superblock at 294912, Group descriptors at 294913-294918
Backup superblock at 819200, Group descriptors at 819201-819206
Backup superblock at 884736, Group descriptors at 884737-884742
Backup superblock at 1605632, Group descriptors at 1605633-1605638
Backup superblock at 2654208, Group descriptors at 2654209-2654214
Backup superblock at 4096000, Group descriptors at 4096001-4096006
Backup superblock at 7962624, Group descriptors at 7962625-7962630
Backup superblock at 11239424, Group descriptors at 11239425-11239430
Backup superblock at 20480000, Group descriptors at 20480001-20480006
Backup superblock at 23887872, Group descriptors at 23887873-23887878
Choose an alternate superblock from this list, for this case alternate superblock # 32768
Now, to check and repair a Linux file system using alternate superblock # 32768:
sudo fsck -b 32768 /dev/sda2 -y
-y flag is used to skip all the
Fix? questions and to answer them all with a yes automatically
You should get similar output like this:
fsck 1.40.2 (12-Jul-2007)
e2fsck 1.40.2 (12-Jul-2007)
/dev/sda2 was not cleanly unmounted, check forced.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
Free blocks count wrong for group #241 (32254, counted=32253).
Free blocks count wrong for group #362 (32254, counted=32248).
Free blocks count wrong for group #368 (32254, counted=27774).
/dev/sda2: ***** FILE SYSTEM WAS MODIFIED *****
/dev/sda2: 59586/30539776 files (0.6% non-contiguous), 3604682/61059048 blocks
Now try mounting the partition
sudo mount /dev/sda2 /mnt
Now, try to browse the filesystem with the following commands
cp file /path/to/safe/location
If you are able to perform the above commands, you have most probably fixed your error.
Now, restart you computer and you should be able to boot normally.
fsckwas run, the same error was shown on boot again.